Postoperative pain is experienced by millions of patients every day throughout the world. Despite the availability of adequate pharmacologic agents, pain is one of the most frequently encountered postoperative problems. Documentation concerning the undertreatment of acute pain as a major health care problem has occurred extensively within the past decade. Recent evidence indicates that health care providers have difficulty accurately assessing a patient's analgesic requirements. Technological advances have led to the development and acceptance of patient-controlled analgesia (PCA) therapy for treatment of postoperative pain. However, minimal research exists concerning the optimal method of drug delivery utilizing PCA therapy. Increasing evidence supports the existence of temporal variations in pain sensitivity and analgesic requirements in postoperative pain. The purpose of this study is to evaluate time- dependent approaches to pain assessment and intervention that may be implemented by health care providers to optimize pain relief. A chronotherapeutic treatment regimen employing a sinusoidal basal infusion pattern will be implemented and evaluated in a randomized double- blind clinical trial designed to compare the efficacy of chronotherapeutic versus demand-only PCA therapy for postoperative pain relief. General surgery and orthopedic surgery patients (N = 200) will be randomly assigned to either a demand-only or chronotherapeutic post-surgical treatment regimen. Patient visual analog scores (VAS) for pain intensity, sedation, attempts at self-administration of analgesic and unfulfilled requests for analgesic will be obtained at 4-hr intervals for a 72-hr period postoperatively. Further, incidence of atelectasis, pruritus, nausea, vomiting, urinary retention, respiratory depression, undersedation, oversedation and length of stay will be obtained by chart review. Data for the first two postoperative days will be analyzed using repeated measures MANCOVA and chi-square analyses to determine if patients receiving a chronotherapeutic PCA regimen have a diminished perception of post.operative pain, fewer unfulfilled requests for analgesic, fewer attempts at self-administration of analgesic during the usual sleep period and a decreased incidence of post-operative complications when compared to patients receiving the standard, demand-only PCA delivery regimen. In addition, the number of attempts of self-administration of analgesic will be correlated with the patient's perception of pain intensity for each time period to evaluate the use of the PCA pump by nurses as a pain assessment instrument to validate patients' perception of post-operative pain. The results of this study will provide health care professionals with a chronotherapeutic regimen for PCA therapy that will be superior in reducing post-surgical pain while concurrently decreasing post-surgical complications.